1. Field of the Invention
The present invention generally relates to test probes for integrated circuit (IC) sockets, and more particularly to a test probe and a manner of making the test probe for insertion into integrated circuit sockets.
2. Background Information
Integrated circuits are commonly made with sockets for receiving semi-conductor chips. During the production process, these sockets are tested to be sure that all of their electrodes are connected and that they mate correctly with the electrodes of the socket to be inserted. To test the IC socket, a test probe is inserted into the socket. The test probe has electrodes which make contact with the electrodes of the socket. The electrodes of the test probe are connected to a testing device which can perform diagnostic testing of the socket and its relation to other circuitry in the IC. These sockets are typically mounted on printed circuit boards (PCB) and many such devices are connected to each other by circuitry in the PCB. An individual socket test probe is inserted into a large number of sockets to be tested during the lifetime of the test probe. These repeated insertions and removals cause wear on the electrodes of the test probe, and finding a design of a socket test probe which provides reliable connections, and durability after repeated insertions, is an ongoing problem. As the number of electrodes in these sockets has increased, the electrodes have become smaller and the spacing between them has also become closer. Therefore, the electrodes of the socket test probe must also be tightly packed together, and yet remain completely isolated from neighboring electrodes, accurately placed, small in width, and extremely durable. Achieving these goals has been difficult in prior art electrodes.
One socket test probe which attempts to resolve this problem is that of Tan, U.S. Pat. No. 5,436,570. Tan utilizes metal pins embedded in resin as the electrodes of a probe head. The sides of the probe head are machined so that the pins are partially exposed. The partially exposed sides of the pins form the electrodes of the probe head. According to Tan, the pins are to be machined so that less than fifty per-cent of their diameter is machined away. In actual practice, it is not uncommon for more than fifty per cent of a pin to be ground through. When this happens, the remaining portion of the pin is not very strongly held in the surrounding resin. After repeated uses, a pin can come loose from the resin and be peeled away from the probe head, and further use of that probe head will damage the sockets being tested.
Accordingly, it is an object of the invention to provide a socket test probe which has the capability of simulating narrow, closely spaced electrodes, but which will be durable for multiple insertions, and is not highly sensitive to machining errors during production.
A further object is a socket tester in which the electrodes do not become dislodged from the probe head and peel away from it.
Another object of the invention is to provide a process for making such a socket probe tester.
A further object of the invention is to provide a socket probe tester with the capability of renewing its electrode surfaces when they show wear.
Additional objects, advantages and novel features of the a invention will be set forth in part in the description as follows, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
These and other objects are attained by a socket test probe, which is designed for attachment to a socket testing device. The socket test probe is utilized in testing electrical sockets which are themselves designed to receive semi-conductor chips on an integrated circuit. The socket test probe includes a probe body, which is a generally square or rectangular piece, generally made of a conductive material. The outside walls of the probe body enclose a central opening which extends throughout its length. Inside the central opening is mounted a generally rectangular test probe. The test probe is mounted inside the probe body by a region of non-conductive resin. The test probe has four sidewalls and includes alternating layers of non-conductive resin and conductive plates, typically made of copper or other conductor. Each plate is generally rectangular and has a top edge, bottom edge, inner edge, and an outer edge. The plates are arranged along one or more sidewalls of the test probe, so that an outer edge of each conductive plate is exposed along the length of the sidewall, and serves as the electrode for the probe. The inner edge and the sides of the conductive plate are enclosed within the resin of the test probe. A bottom edge of the test probe is connected to an electrical connection, typically a copper wire attached to the conductive plate. One end of the test probe forms a four-sided test probe head, and the other end of the test probe terminates with exposed ends of the conductive plates where they attach to electrical connectors. The exposed plate edges and/or plate top edges form the electrodes along one or more sides of the probe head, or along the top of the probe head. The electrical connectors terminate in a probe interface, which is mounted to the probe body adjacent to the ends of the conductive plates.
The probe body can contain one or more positioning holes, or holes in the probe body can be mounted with a positioning pin. The positioning holes or pins in the probe body are configured to connect with matching positioning holes or pins in a testing device, which is designed to receive the test probe. The probe interface of the device typically is made from printed circuit board type material. On the probe interface are interface connection positions in which the second end of the wire is encased by solder knobs. The socket test probe described above can also have probe heads which are not perfectly rectangular in shape, but can fit any particular socket shape. The edges of the probe head can be beveled, or they can include a protrusion along the lower rim to simulate a xe2x80x9cgull wingxe2x80x9d or xe2x80x9clive bugxe2x80x9d semi-conductor chip. The probe head can also include a ridge on each of the electrodes and resin layer to simulate a xe2x80x9cdead bugxe2x80x9d type semi-conductor chip, which uses a xe2x80x9cround knobxe2x80x9d connection. The probe head can also include multiple examples of these ridges, flares and other probe head tip shapes. The purpose of multiple spaced-apart protrusions such as this is so that when electrode surfaces being utilized show signs of wear, they can be machined down to expose a new set of electrode surfaces which also have a xe2x80x9cgull wingxe2x80x9d or other configuration. The socket testing probe described above can also have one or more holes which pass through the conductive plates, and which is filled with resin. This makes the resin contiguous from each side of one plate to another, and aids in preventing delamination of the conducting plates from the resin.
Another aspect of the invention is the method of making the socket test probe. These steps start with a solid rectangular block of conductive metal, such as copper, and machining a recess on one end of the block. This recess leaves an outer rim around the end, and defines a moat around a rectangular tower of metal from the original solid block of metal. The next step is drilling a central hole through the tower of metal and all the way through the block to the other side. Starting from the central hole just drilled, the hole is expanded into a central channel with fluted side channels which define three sides of a number of plates. Electro-discharge machining (EDM) has been found to be highly effective for this machining, although other methods could work just as well, such as high pressure water jet cutting or plasma cutting. The central channel and fluted side channels define three sides of a number of conductive plates. At this point, the fourth side of each plate is still attached to the original block of metal which was the starting point. After the central channel has been machined by EDM, electrical connectors are attached to these ends of the conductive plates which protrude into the recess. Then the central channel and part of the recess in the block is filled with a liquid resin. During the filling, precautions are taken to remove bubbles from the resin. This can be by a vibration, by filling slowly from the bottom, or by the use of a highly viscous resin, or by use of a vacuum chamber. The recess is filled to a level even with corner bosses in the recess, covering all the conductive plates. Next, the remaining block of metal is machined on the second end of the metal block down to the resin core which is in the central channel of the block. By machining down to this resin core, a rectangular test probe is left, with the outside edges of the conductive plates exposed and forming electrodes for contact with a socket. This machining is extended slightly into the moat now filled with resin, thereby isolating the conductive plates from contact with the metal block from which they originated and leaving the metal plates encased in resin. Each has an outside edge exposed, to serve as an electrode, and is connected to the metal block by the remaining resin in the moat. The end of the block opposite the recess now forms a probe head. The next step is connecting the electrical connections to a probe interface for communication with a matching interface of a testing device. The electrical connectors are typically copper wires, and are connected to the probe interface by putting the wires through holes in the PC board, stripping the wires, pushing the wires back into the PC board, soldering the wires to the PCB, and trimming the wires, which leaves a solder knob on the outside of the PC board and the probe interface.
The method can also include the step of drilling one or more positioning holes in the rim around the recess of the metal block. The hole can be used to mount a positioning pin, or the hole can interconnect with a positioning pin from corresponding pins in a testing device designed to connect with the test probe. An optional step can include machining the probe head of the metal block to leave a protrusion on the outer edge which makes the electrodes of the probe head similar in shape to semi-conductor chips with flared electrodes. A number of these protrusions can be arranged in spaced apart positions on the test probe, so that when one becomes worn, it can be machined away and the next electrode set can be utilized. The method can also involve machining the probe head edge to form a beveled edge. The method can also involve drilling one or more holes through the metal block, so that the hole passes through the conductive metal plates. When the central channel is filled with resin, the resin passes through the holes and connects the conductive plates together with a contiguous resin rod. This contiguous resin rod helps resist delamination of the layers of the conductive plates and the resin layers.
Still other objects and advantages of the present invention will become readily apparent to those skilled in this art from the following detailed description wherein I have shown and described only the preferred embodiment of the invention, simply by way of illustration of the best mode contemplated by carrying out my invention. As will be realized, the invention is capable of modification in various obvious respects all without departing from the invention. Accordingly, the drawing and description are to be regarded as illustrative in nature, and not as restrictive.